Setting the `JackUp.Processor` path to `/assets.json` made it not include the
file in the params. Without the `.json`, it correctly saved the Asset record
with the attached file, but then returned a 406 "content not acceptable" error
since the controller only responds to JSON, and it was processed as HTML.
This way it accepts the HTML request and returns JSON to JackUp.

Setting the `JackUp.Processor` path to `/assets.json` made it not include the
file in the params. Without the `.json`, it correctly saved the Asset record
with the attached file, but then returned a 406 "content not acceptable" error
since the controller only responds to JSON, and it was processed as HTML.
This way it accepts the HTML request and returns JSON to JackUp.